Switched reluctance generator with improved generation efficiency in low-speed range

ABSTRACT

Disclosed is an SR (switched reluctance) generator with improved generation capability in a low-speed range. The SR generator is configured such that an inductance of a phase winding wound around a stator is increased in a low-speed range and is reduced in a high-speed range. Accordingly, a variation rate of the inductance relative to a phase angle is increased in a low-speed range, resulting in an increased output energy in a low-speed range and an improved generation efficiency. The phase winding of the stator may be configured to have a single phase. Accordingly, since the generator is configured with the reduced number of switches, it can be manufactured inexpensively and simply.

BACKGROUND OF THE INVENTION

This application claims the priority of Korean Patent Application No.2005-27620, filed on Apr. 1, 2005, in the Korean Intellectual PropertyOffice, the disclosure of which is incorporated herein in its entiretyby reference.

1. Field of the Invention

The present invention relates to a switched reluctance (SR) generatorand, more particularly, to an SR generator with improved generationcapability in a low-speed range.

2. Description of Related Art

An SR generator is an energy conversion device which, through electronicswitching, applies electrical energy from a voltage source to a windinghaving at least one phase over a prescribed range of rotor angle andreceives back from the phase winding over a later range of rotor angle alarger quantity of energy than previously applied. This additionalenergy is mechanical energy, imparted to the generator rotor by applyinga torque in the direction of rotation. Such an SR generator isadvantageous in that it can generate energy in a low-speed range sinceit outputs in a form of a current source.

Conventionally, induction generators or synchronous generators have beenused as wind generators. The induction generator is simple in structureand is inexpensive, while there are disadvantages in that it needs anadditional gear box to keep a constant speed upon generating electricityand a speed range of wind necessary to generate electricity is limited.Meanwhile, there are disadvantages in that the synchronous generator iscomplex in structure and is expensive. In addition, in the synchronousgenerator, a battery is not charged at low wind speeds since voltageoutputted from the generator is small. Accordingly, it is very difficultto generate electricity using the induction generators or synchronousgenerators in an area where the wind speed is low, such as in Korea.While developing a generator that is able to efficiently generateelectricity by wind power even in a low-speed range, the presentinventor has found it possible to improve the SR generator to be appliedto such an area.

SUMMARY OF THE INVENTION

The present invention provides an SR generator capable of generatingelectricity in a low-speed range.

The present invention further provides an SR generator that is simple instructure and is durable.

According to an aspect of the present invention, there is provided an SRgenerator which is configured such that an inductance of a phase windingwound around a stator is increased in a low-speed range and is reducedin a high-speed range.

Accordingly, a variation rate of the inductance relative to a phaseangle is increased in a low-speed range, resulting in an increasedoutput energy in a low-speed range and an improved generationefficiency.

The phase winding of the stator may be configured to have a singlephase. Accordingly, since the generator is configured with the reducednumber of switches, it can be manufactured inexpensively and simply.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings in which:

FIG. 1 is a block diagram showing a construction of an SR generator inaccordance with an embodiment of the present invention;

FIG. 2 is a graph showing relations between a phase inductance of arotor relative to a phase angle and a generating current and a motoringcurrent in an SR generator;

FIG. 3 is a view showing a connection structure of a single-phase statorin an SR generator in which a phase winding is made up of three unitwindings;

FIG. 4A is a view showing a connection method of the stator having theconnection structure shown in FIG. 3 in a low-speed range, and FIG. 4Bis a view showing a connection method of the stator in a high-speedrange;

FIG. 5A is a view showing a relation between an inductance and agenerating current in a low-speed range in the stator having theconnection structure shown in FIG. 3, and FIG. 5B is a view showing arelation between an inductance and a generating current in a high-speedrange in the stator shown in FIG. 3; and

FIG. 6 is a graph showing the amount of generated energy relative towind speed in an SR generator according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary embodiments in accordance with the present invention will nowbe described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing a construction of an SR generator inaccordance with an embodiment of the present invention. As shown in FIG.1, the SR generator includes a rotor 10, a stator 30 around which aphase winding is wound, a drive switch 100 controlling current flowingin the phase winding 300, and a power controller 500 controllingswitching of the drive switch 100. The SR generator is configured suchthat an inductance of the phase winding 300 becomes larger in alow-speed range and becomes smaller in a high-speed range.

The SR generator according to an embodiment of the present inventionincludes the phase winding 300 having a plurality of unit windings 310,330, 350 and at least one winding switch 340, 360connecting/disconnecting the unit windings to one another, a speeddetector 530 detecting a rotation speed of the rotor, and a connectioncontroller 700 controlling switching of the winding switches 340, 360according to the speed detected by the speed detector 530 so that theinductances of the windings become larger in a low-speed range andbecome smaller in a high-speed range.

Meanwhile, a single-phase SR generator requires an initial excitationcurrent. For this purpose, a stand-alone generation system drives asmall-sized synchronous motor provided parallel to a generator to supplynecessary power. In FIG. 1, a current source 910 and a capacitor 930 areshown to represent such an initial excitation current system. In thepresent embodiment, the phase winding 300 of the stator is asingle-phase winding. The single-phase SR generator can be produced at alow price since it needs only a few switches for energy conversion.However, the present invention is not limited thereto.

Through electronic switching of the drive switch 100, the phase winding300 receives an electrical energy from the capacitor 930, a voltagesource, over a prescribed range of rotor angle and supplies to a battery955 over a later range of rotor angle a larger quantity of energy thanpreviously received. The power controller 500 controlling the electronicswitching of the drive switch 100 outputs a pulse-width modulationsignal to control the electronic switching according to the position ofthe rotor detected by the speed detector 530. In addition, the powercontroller 500 adjusts the pulse-width modulation signal to preventovercurrent by detecting an output current of the generator through thecurrent detector 510. Meanwhile, various types of power controllers 500are well known in the art. In addition, various types of speed detectors530 using a hall sensor or a current detection method are well known inthe art. For example, the speed detector 530 can detect the speed bydetecting and differentiating a displacement or by counting a sequenceof pulses outputted from an encoder for a predetermined time interval.

According to the present embodiment, the SR generator further includes abattery 955 to which a current outputted from the phase winding 300 ofthe stator is charged, and a step-up DC-AC inverter 400 stepping up anoutput voltage of the battery 955. The output of the inverter 400 issupplied to a load 600. Diodes 951, 953 act to prevent the electricalpower charged to the battery from flowing backward to the phase winding.

Operation of the connection controller 700 according to the presentinvention will now be described with reference to FIG. 1. The connectioncontroller 700 controls switching of the winding switches 340, 360 inthe phase winding 300 according to the speed detected by the speeddetector 530 to change a connection method of the unit windings 310,330, 350.

A voltage equation of the SR generator is expressed as follows:$\begin{matrix}{{v = {{{Ri} + \frac{\mathbb{d}\phi}{\mathbb{d}t}} = {{{Ri} + {L\frac{\mathbb{d}i}{\mathbb{d}t}} + {i\frac{\mathbb{d}\theta}{\mathbb{d}t}\frac{\mathbb{d}L}{\mathbb{d}\theta}}} = {{Ri} + {L\frac{\mathbb{d}i}{\mathbb{d}t}} + e}}}}\quad{where}} & \left\lbrack {{Equation}\quad 1} \right\rbrack \\{e = {{i\frac{\mathbb{d}\theta}{\mathbb{d}t}\frac{\mathbb{d}L}{\mathbb{d}\theta}} = {{\mathbb{i}\omega}_{m}\frac{\mathbb{d}L}{\mathbb{d}\theta}}}} & \left\lbrack {{Equation}\quad 2} \right\rbrack\end{matrix}$Thus, the energy flow is expressed as follows: $\begin{matrix}{{vi} = {{{Ri}^{2} + {{Li}\frac{\mathbb{d}i}{\mathbb{d}t}} + {i^{2}\frac{\mathbb{d}\theta}{\mathbb{d}t}\frac{\mathbb{d}L}{\mathbb{d}\theta}}} = {{Ri}^{2} + {\frac{\mathbb{d}}{\mathbb{d}t}\left( {\frac{1}{2}{Li}^{2}} \right)} + {\frac{1}{2}i^{2}\omega_{m}\frac{\mathbb{d}L}{\mathbb{d}\theta}}}}} & \left\lbrack {{Equation}\quad 3} \right\rbrack\end{matrix}$where the first term indicates a copper loss, the second term indicates{core loss+magnetic energy}, and the third term indicates a mechanicaloutput, a generation power. It is operated as a motor over a range ofdL/dθ>0 since the mechanical output is positive (+) . Meanwhile, it isoperated as a generator over a range of dL/dθ>0 since the mechanicaloutput is negative (−). FIG. 2 is a graph showing relations between aphase inductance of a rotor relative to a phase angle and a generatingcurrent and a motoring current in the SR generator. As shown in FIG. 2,the inductance has a maximum value Lmax at θ=θmax, while the inductancehas a minimum value Lmin at θ=θmin.

The connection controller 700 according to an embodiment of the presentinvention controls a connection between the respective unit windings sothat the respective unit windings are connected in series to each otherin a low-speed range and connected in parallel to each other in ahigh-speed range. FIG. 1 shows an embodiment in which the single-phasephase winding 300 is made up of three unit windings 310, 330, 350 andtwo winding switches 340, 360 controlling a connection between the threeunit windings. FIG. 3 shows a connection structure of the stator in theSR generator. In this embodiment, the unit windings are assigned to therespective groups consisting of the equal number of adjacent statormagnetic poles equally divided from the stator magnetic poles which areradially arranged. At this time, the respective unit windings are woundaround the stator so that polarities of adjacent magnetic poles in therespective groups are alternated with each other. That is, therespective magnetic poles have polarities opposite to those of adjacentmagnetic poles. The magnetic poles are divided by the three unitwindings into three groups of magnetic poles each of which is wound by asingle unit winding. In FIG. 3, the symbol “o” or “x” denotes a wounddirection. Increasing the number of magnetic poles and improving aconnection method of windings make it possible to achieve a higherenergy efficiency in a low-speed range.

FIG. 4A shows a connection method of the stator having the connectionstructure shown in FIG. 3 in a low-speed range. FIG. 4B shows aconnection method of the stator in a high-speed range. FIG. 5A shows arelation between an inductance and a generating current in a low-speedrange in the stator having the connection structure shown in FIG. 3.FIG. 5B shows a relation between an inductance and a generating currentin a high-speed range in the stator having the connection structureshown in FIG. 3.

As shown in Equation 3, the energy generated in the SR generator isexpressed as follows: $\begin{matrix}{{Energy} = {\frac{1}{2}i^{2}\omega_{m}\frac{\mathbb{d}L}{\mathbb{d}\theta}}} & \left\lbrack {{Equation}\quad 4} \right\rbrack\end{matrix}$

As can be seen from an inductance profile shown in FIG. 5A, since theunit windings are connected in series to each other in a low-speedrange, the inductance becomes large. Thus, since Lmax and Lmin areincreased, dL/dθ becomes large, thereby increasing generationefficiency. Further, in terms of an excitation current, Lmax is large ina low-speed range. However, since the speed is low, a time periodrequired for excitation is sufficiently allowed so that a sufficientexcitation current can be obtained. Accordingly, the sufficient amountof energy can be generated in a low-speed range since dL/dθ is largedespite a low angular speed w.

Meanwhile, since the unit windings are connected in parallel to eachother in a high-speed range, the inductance is reduced. Thus, since Lmaxand Lmin are reduced, dL/dθ becomes small. However, since the angularspeed w is large, the sufficient amount of energy can be generated in ahigh-speed range. FIG. 6 is a graph showing the amount of generatedenergy relative to wind speed in an SR generator according to anembodiment of the present invention. It can be seen from a dotted areashown in the drawing that generation efficiency has been improved in alow-speed range.

As apparent from the above description, the SR generator according tothe present invention is configured such that the inductance of thephase winding wound around the stator is increased in a low-speed rangeand is reduced in a high-speed range. Accordingly, since a variationrate of the inductance relative to the phase angle becomes large in alow-speed range, output energy is increased in a low-speed range,thereby improving generation efficiency.

Further, the SR generator according to the present invention isconfigured such that the phase winding of the stator is configured tohave a single phase. Accordingly, the number of switches is reduced,thereby reducing the cost.

While the present invention has been described with reference toexemplary embodiments thereof, it will be understood by those skilled inthe art that various changes in form and details may be made thereinwithout departing from the scope of the present invention as defined bythe following claims.

1. A switched reluctance (SR) generator comprising a stator having aphase winding, the phase winding being wound around the stator such thatit has an inductance becoming large in a low-speed range and small in ahigh-speed range.
 2. The SR generator of claim 1, wherein the phasewinding includes: a plurality of unit windings; and at least one windingswitch for switching a connection between the unit windings.
 3. The SRgenerator of claim 2, wherein the winding switch connects the unitwindings in series in the low-speed range and in parallel in thehigh-speed range.
 4. The SR generator of claim 2, further comprising: aspeed detector for detecting a rotation speed of a rotor correspondingto the stator; and a connection controller for controlling the switchingof the winding switch according to the speed detected by the speeddetector such that the inductance of the phase winding becomes large inthe low-speed range and small in the high-speed range.
 5. The SRgenerator of claim 4, wherein the winding switch connects the unitwindings in series in the low-speed range and in parallel in thehigh-speed range under the control of the connection controller.
 6. TheSR generator of claim 4, further comprising: a battery for chargingitself with an output current from the phase winding of the stator; anda step-up DC-AC inverter for stepping up an output voltage from thebattery.
 7. The SR generator of claim 1, wherein the phase winding is asingle-phase winding.
 8. The SR generator of claim 7, wherein the phasewinding includes: a plurality of unit windings; and at least one windingswitch for switching a connection between the unit windings.
 9. The SRgenerator of claim 8, wherein each of the unit windings of the phasewinding is assigned to a corresponding one of a plurality of groups ofmagnetic poles of the stator so as to be wound around the correspondinggroup such that adjacent ones of the magnetic poles in the correspondinggroup have alternating polarities, the magnetic poles of the pluralityof groups being radially arranged and being equally divided in number toconstitute corresponding ones of the groups, respectively.
 10. The SRgenerator of claim 8, further comprising: a speed detector for detectinga rotation speed of a rotor corresponding to the stator; and aconnection controller for controlling the switching of the windingswitch according to the speed detected by the speed detector such thatthe inductance of the phase winding becomes large in the low-speed rangeand small in the high-speed range.
 11. The SR generator of claim 10,wherein the winding switch connects the unit windings in series in thelow-speed range and in parallel in the high-speed range under thecontrol of the connection controller.
 12. The SR generator of claim 10,further comprising: a battery for charging itself with an output currentfrom the phase winding of the stator; and a step-up DC-AC inverter forstepping up an output voltage from the battery.
 13. An SR generatorcomprising: a rotor; a stator having a phase winding wound therearound;a drive switch for controlling current flowing in the phase winding; anda power controller for controlling switching of the drive switch,wherein the phase winding is wound around the stator such that it has aninductance becoming large in a low-speed range and small in a high-speedrange.
 14. The SR generator of claim 13, wherein the phase windingincludes: a plurality of unit windings; and at least one winding switchfor switching a connection between the unit windings.
 15. The SRgenerator of claim 14, further comprising: a speed detector fordetecting a rotation speed of the rotor; and a connection controller forcontrolling the switching of the winding switch according to the speeddetected by the speed detector such that the inductance of the phasewinding becomes large in the low-speed range and small in the high-speedrange.
 16. The SR generator of claim 15, wherein the connectioncontroller controls the switching of the winding switch such that thewinding switch connects the unit windings in series in the low-speedrange and in parallel in the high-speed range.
 17. The SR generator ofclaim 13, wherein the phase winding of the stator is a single-phasewinding.
 18. The SR generator of claim 17, wherein each of the unitwindings is assigned to a corresponding one of a plurality of groups ofmagnetic poles of the stator so as to be wound around the correspondinggroup such that adjacent ones of the magnetic poles in the correspondinggroup have alternating polarities, the magnetic poles of the pluralityof groups being radially arranged and being equally divided in number toconstitute corresponding ones of the groups, respectively.
 19. The SRgenerator of claim 15, further comprising: a battery for charging itselfwith an output current from the phase winding of the stator; and astep-up DC-AC inverter for stepping up an output voltage from thebattery.